The invention relates to improvements to television cameras and more specifically to an anti-blooming device for equipping such a camera. The invention more specifically applies in an advantageous manner to systems for the guidance of missiles by television.
The device is intended to prevent the effect of blooming produced at the camera tube of a television camera by a very bright object present in the observed scene. The sensitivity of the tube, such as a vidicon, is a function of the nature of the photosensitive layer (quantum efficiency, spectral band) and the charge storage time. When a very bright spot focused on the tube produces illumination exceeding the saturation limit of the photoreceiving target, the image obtained on a TV monitor associated with the camera is widened in the form of a stain, whose size increases with the brightness of the bright spot compared with the saturation illumination of the camera tube. This effect is called blooming.
This phenomenon can be very prejudicial to operation, because the thus formed stain can mask parts of the image which are particularly important for the envisaged mission. This is particularly the case with missile guidance systems by television when the bright spot constituted by the missile masks the tracked target (to prevent any confusion the photosensitive target of the tube will be called retina hereinafter). The bright spot is constituted by gases emitted by the rocket propulsion system, which may also have a tracer device constituted by a complementary pyrotechnic charge. Television guidance of the missile can, for example, take place in the following way. The television camera supplies an image of the scene which is visually utilized by the operator, who maintains the sighting axis (centre of the TV image) pointed on the target tracked from the image present on the monitor. As an automatic tracking system is also associated with the missile, it is clear that the widened image of the missile will mask the target when located in the vicinity of the sighting line.